WO1997039263A1

WO1997039263A1 - Ring-shaped sealing element

Info

Publication number: WO1997039263A1
Application number: PCT/EP1997/001927
Authority: WO
Inventors: Martin Struschka; Ulrich Beier
Original assignee: Lucas Industries Public Limited Company; Contitech Formteile Gmbh
Priority date: 1996-04-17
Filing date: 1997-04-17
Publication date: 1997-10-23
Also published as: JP4104169B2; DE59704536D1; ES2163150T3; KR19990087806A; DE19615157A1; KR100433840B1; EP0894213A1; EP0894213B1; JP2000508414A

Abstract

A ring-shaped sealing element (16) for sealingly closing a ring-shaped gap between the inner surface of a cylindrical wall and a concentric cylindrical piston which slides therein in the axial direction has two separate ring-shaped, axially adjacent parts (42, 44), of which the first part (42) is made of an elastomer material and the second part (44) of a stiff material. In order to ensure a as constant as possible opening and closing behaviour of a valve in co-operation with a sliding valve body, the two parts (42, 44) are releasably linked to each other and the part (44) made of stiff material forms a single piece with a ring-shaped, continuous axial projection (46) which extends almost completely through the part (42) made of elastomer material and has a face completely covered by the part (42) made of elastomer material. The ring-shaped, continuous axial projection (46) is designed and arranged in such a way that a radial wall thickness Si of part (42) made of elastomer material at its inner flank in the radial direction is approximately the same as a radial wall thickness Sa at its outer flank in the radial direction. The radial dimension S of the projection (46) equals maximum 70 % of the sum of the wall thicknesses Si + Sa.

Description

Annular sealing element

The invention relates to an annular sealing element according to the preamble of claim 1.

Sealing elements with a rigid support component and an elastomer part arranged thereon are known in principle. In cooperation with valve members, there is the problem that the opening and closing time of a valve is not exactly defined, since the part of the valve which causes the valve to open and close due to its displacement depends on it acting fluid pressure more or less far into the elastomer material of the sealing element, whereby the opening and closing time of the valve varies. This is undesirable in many applications, since the valve should have a constant, precisely defined opening and closing behavior.

A sealing element according to the preamble of claim 1 is known from US Pat. No. 3,282,594. A similar sealing element is known from GB 2 256 687 A. Both sealing elements have in common that the elastomer component of the sealing element is integrally molded with the rigid support body. This is to ensure a good seal between the elastomer material and the material of the rigid support body.

The invention is based on the object of providing an annular sealing element which is suitable for interacting with a displaceable valve body of a valve and in particular for ensuring that the opening and closing behavior of the valve is as constant as possible. With regard to use in large series production, the sealing element should also be inexpensive to manufacture without the

Sealing function of the sealing element is adversely affected. Starting from an annular sealing element of the type mentioned at the outset, this object is achieved according to the invention in that the part made of rigid material and the part made of elastomer material are releasably connected to one another on the

Part made of rigid material, annular circumferential projection only almost completely penetrates the part made of elastomer material axially, the part made of elastomer material completely covers the end face of the projection, and the wall thickness Sj_ is approximately equal to the wall thickness S _a . By "almost completely" is meant here that the axial, free end of the ring-shaped projection formed on the part made of rigid material is not located in the end face of the elastomer part, but somewhat below it, ie that the elastomer part, which ches covers the lead, the latter dominates. The thin elastomer layer thus created, which rests on the front free end of the projection, ensures that a movable valve body always lies softly and slightly dampened on the end face of the sealing element facing it and then, after a negligible compression phase, practically without delay on the Can support part formed of rigid material projection. Due to the support achieved in this way, a defined opening of the valve is ensured regardless of the pressure against which the valve must be opened.

The described design of the sealing element according to the invention leads to a quasi-rigid stop for the displaceable valve body, without the sealing function of the sealing element therefore suffering. On the contrary, the complete overlap of the projection formed on the rigid part of the sealing element by the elastomer part ensures excellent tightness even under critical conditions. Since the greatest radial extension of the circumferential projection is only approximately at most 70% of the sum of the wall thicknesses S ^ and S _a and the wall thicknesses Si and S _{a are} approximately the same, sufficient elastomer material remains radially inside and radially outside the projection for a good, also radially elastic seal. The radial extent of the circumferential projection is preferably only at most about 50% of the sum of the wall thicknesses S 1 + S _a .

The annular circumferential projection of the part made of rigid material can, for example, have the shape of a closed circular ring. Alternatively, the annular circumferential projection can be formed by a plurality of circular ring segments, between which space is left for connecting webs. According to a further modification, at least the free end of the annular circumferential projection can be formed by a series of pin-shaped extensions which are preferably evenly spaced apart from one another in the circumferential direction and which extend axially. In such an embodiment, the quasi-rigid stop is formed by an annular arrangement of approximately punctiform contact surfaces.

According to one embodiment, the elastomer part has on its free end face several, preferably dome-shaped elevations spaced apart from one another in the circumferential direction. With such an embodiment, an even gentler, better damped engagement of the displaceable valve body with the sealing element is achieved, since the valve body only comes into contact with the elastomer part at certain points at the beginning of the engagement, but then immediately after a rapidly increasing resistance bumps. If the annular circumferential projection on the rigid part of the sealing element is formed by a series of pin-shaped projections, the preferably dome-shaped elevations on the free end face of the elastomer part are preferably above the pin-shaped

Processes, i.e. arranged in the axial continuation of the same.

Irrespective of the design of the annular circumferential projection, the radial extension of the projection towards its free end is preferably reduced. The radial extent of the projection can be reduced continuously or in steps. By reducing the Ra- dialer extension an even better sealing effect is achieved, since to the free end of the projection radially inside and radially outside the same, there is increasingly more elastomer material, which results in better radial compensation of the sealing element in the area of its elastomer part.

The part made of rigid material of the sealing element preferably has a hollow cylindrical extension on its end face facing away from the part made of elastomer material. This extension serves to better guide the displaceable piston.

In order to ensure a good sealing effect of the sealing element even at higher pressure, its part made of rigid material should in particular not have any passage recesses in the area with which it rests on the part made of elastomer material.

Areas of the elastomer part could otherwise press into such passage recesses with a corresponding pressure load, as a result of which elastomer material would be missing at other sealing points.

The annular sealing element according to the invention is particularly suitable for use in a master cylinder of a hydraulic vehicle brake system. Such a master cylinder, which is often also called a master brake cylinder, has a housing with a bore extending along a longitudinal axis, one end of which extends from a bore belonging to the housing of the master cylinder

End wall and the other, opposite end is closed by an annular sealing element. An axially displaceable piston, which is arranged concentrically to the bore and has a central valve which has a fluid connection between one, is sealingly guided through the sealing element

Fluid reservoir and a pressure chamber limited in the bore by the end wall and the piston. When the piston is not actuated, the central valve is held in the open position by a system component acting on the sealing element. A master cylinder, in which the annular sealing element is formed from two separate, annular and axially adjoining parts, the first of which faces the bore Part of an elastomeric material and the second part facing away from the bore consists of a rigid material is known from EP 0 467 021 AI.

Master cylinders of this type are used in vehicles primarily together with brake pressure control systems, these brake pressure control systems nowadays frequently having both the function of preventing the vehicle wheels from locking when braking (so-called anti-lock braking system) and the function of spinning the drive wheels to prevent when accelerating, especially on slippery surfaces (so-called anti-slip regulation). As already mentioned, the central valve arranged in the piston is in the unactuated state of the master cylinder, i.e. when the piston is in its rest or starting position, it is kept open by a contact component connected to the central valve, which is supported directly or indirectly on the end face of the part of the closure element made of elastomer material belonging to the closure element.

The central valve is opened in that the system component connected to it comes into contact with the end face of the closure element facing the system component and is supported there during the return movement of the piston after its actuation of the master cylinder, which leads to the opening of the central valve. This means that the central valve must be opened against the pressure prevailing in the pressure chamber at this point in time. In normal driving, it is often the case that at the point in time at which the system component lies against the closure element, there is no or only a slight excess pressure in the pressure chamber. Under certain circumstances, however, it may happen that the central valve still has to be opened against a considerable excess pressure, in particular when braking is required immediately after an anti-slip control cycle and the master cylinder is therefore actuated. In such a case, the fluid pressure built up in the pressure chamber of the main cylinder as part of the anti-slip control has there is no longer any opportunity for the brake actuators to relax, since the additional fluid volume which was supplied to the pressure chamber during the anti-slip control cycle to build up pressure cannot be returned to the fluid storage container due to the brake actuation which immediately follows in time. Depending on the fluid pressure still prevailing in the pressure chamber, however, the opening time of the central valve varies since the system component connected to the central valve penetrates deeper into the elastomer part of the closure element, the higher the pressure then prevailing in the pressure chamber and the central valve can only open when there is a corresponding counterforce exerted by the closure element on the system component. A clear definition of the opening time of the central valve in relation to the piston arranged in the bore of the master cylinder is therefore not possible, instead the central valve opens earlier and later depending on certain operating conditions. This is undesirable for reasons of constant brake response behavior.

Two exemplary embodiments of a sealing element according to the invention are explained in more detail below with reference to the attached figures. It shows:

Fig. 1 shows a longitudinal section through the end portion of a

Master cylinder in an enlarged view, in which a first embodiment of a sealing element according to the invention is used,

Fig. 2 shows a cross section through that used in Fig. 1

Sealing element in an enlarged view, and

3 shows a view corresponding to FIG. 2 of a sealing element modified compared to FIGS. 1 and 2.

In Fig. 1, the force input end of a generally designated 10 master cylinder for a hydraulic vehicle brake system shown. The master cylinder 10 has an elongated housing 12 with a bore 14 running along a longitudinal axis A and in the embodiment shown stepped. The end (not shown here) of this bore 14 is usually from one to the housing 12 of the master cylinder 10 belonging front wall tightly closed. The other end of the bore 14 opposite this end is sealed as shown with a closure or sealing element 16, the structure of which will be explained in more detail later.

In the bore 14, adjacent to the sealing element 16, a piston 18 which can be actuated through the latter is received in a sealing and axially displaceable manner. In the piston 18 there is a central valve 20 with a valve seat 22 and a spring in

Arranged on the valve seat 22 biased, axially movable valve body 24. In the illustrated, opened state, the central valve 20 releases a fluid connection between a fluid reservoir (not shown), which is connected to the follow-up bore 26, and a pressure chamber 28, which is not in the bore 14 between the piston 18 and the one shown, closed one end of the bore 14 is limited. The piston 18 is shown in the figure in its rest or initial position, which it assumes in the unactuated state and in which it is biased in the usual way by a return spring 30. The parts of the master cylinder 10, not shown, are of conventional, known design and are therefore not explained in detail. In addition to the piston 18 shown, a similarly constructed second piston can be found in the part of the master cylinder 10 which is not shown and which is then referred to as the secondary piston.

The valve body 24 of the central valve 20 has a pin-shaped extension 32 which extends through the piston 18 and at the free end of which extends as a stop component

Cross pin 34 is attached. The cross pin 34 is in one piece with the play in a radial through recess 36 Piston 18 connected actuation extension 38 of reduced diameter received, which extends through the sealing element 16, protrudes from the housing 12 of the master cylinder 10 and is provided for connection to a rod-shaped input member, not shown. When the piston 18 assumes the rest position shown, the transverse pin 34 bears against a stop ring disk 40, which in turn is in contact with the end face of an elastomer part 42 belonging to the sealing element 16, so that the central valve 20 is held in the open position.

In addition to the annular elastomer part 42, the sealing element 16 has an axially adjoining, separate and also annular part 44 made of rigid material, for example of a suitable, hard plastic. On its end face facing the elastomer part 42, the part 44 made of rigid material has an annular circumferential, axially extending projection 46 which is completely covered by the elastomer part 42 and which in the example shown tapers conically towards its free end, whereby its free end, in accordance with the first embodiment shown in FIGS. 1 and 2, is formed by a series of pin-shaped extensions 48 which are evenly spaced apart from one another in the circumferential direction and which likewise extend axially. As can be seen better from FIG. 2, the

Axial extent of the projection 46 (including its extensions 48) is selected such that the elastomer part 42 is almost completely penetrated axially by the projection 46. Between the end face of the elastomer part 42 in contact with the stop ring disk 40 and the end face surface of each of the pin-shaped extensions 48 there is only a thin elastomer layer of thickness D (see FIG. 2). As can be seen from FIG. 3, the radial inner section of the elastomer part 42 adjoining the projection 46 has a radial wall thickness S and the radially outer section of the elastomer part 42 adjoining the projection 46 has a radial wall thickness S _a , where S 1; and Sα_ have approximately the same value. The biggest Ra dialer extension S of the projection 46, which in the exemplary embodiment shown is due to the conical configuration of the projection 46 at its base, is approximately 50% of the sum of the wall thicknesses S and S here. As can also be seen from FIG. 3, a series of dome-shaped elevations 49 are formed in one piece with the elastomer part 42 on the free end face of the elastomer part 42. Each dome-shaped elevation 49 is arranged exactly above one of the pin-shaped extensions 48 of the projection 46.

The parts 42 and 44 of the sealing element 16, which are inexpensive to produce due to the separate design, are detachably connected to one another by joining them together. The sealing element 16, the part 44 of which, in the example shown, has an integrally molded, hollow-cylindrical extension 50 for better guidance of the actuating extension 38, is held in the step-widened end section of the bore 14 of the master cylinder 10 by a snap ring 52 arranged in a circumferential groove.

The function of the master cylinder 10 shown is as follows: starting from the initial position shown of all parts, when the brake system is actuated by the driver, the piston is moved via the rod-shaped input member, not shown, which is connected to the actuation extension 38 of the piston 18 18 relative to the housing 12 of the master cylinder 10 shifted to the left in relation to the figure. The cross pin 34, which keeps the central valve 20 open in the unactuated state of the master cylinder, is released from the stop ring disk 40 and the central valve 20, which is spring-biased in the closing direction, closes, after which, according to the further axial displacement of the piston 18, fluid pressure in the pressure chamber 28 is built. During such actuation of the main cylinder 10, the sealing element 16 takes over both the sealing of the bore 14 with respect to the actuation extension 38 and its guidance. The relaxation movement when the brake is released takes place accordingly in the reverse order, ie the piston 18 moves under the action of the return spring 30 to the right in relation to the figure and the cross pin 34 comes into contact with the stop shortly before the piston 18 reaches the rest position ¬ washer 40, so that the central valve 20 opens again and a possibly existing, low residual pressure in the pressure chamber 28 is discharged via the trailing bore 26 into the fluid reservoir, not shown.

In the following, it is to be assumed that an anti-slip control cycle expired shortly before a brake actuation by the driver, within the scope of which an additional fluid volume was automatically supplied from the fluid reservoir to the pressure chamber 28 in order to provide brake pressure to reduce the wheel slip . If a brake application is initiated by the driver immediately following such an anti-slip control cycle, the central valve 20 must be opened at the end of the braking against a partially considerable overpressure, since a pressure release in the pressure chamber 28 by a feedback of the supplied during the anti-slip control cycle , additional fluid volume in the fluid reservoir was no longer possible before the directly subsequent brake application initiated by the driver. Depending on the size of the fluid volume supplied during the anti-slip control cycle, there is still a more or less overpressure in the pressure chamber 28 even when the piston 18 has returned to its starting position after the brake application initiated by the driver has ended . Even in such a case, however, the opening time of the central valve 20 changes only insignificantly, since the pressure transmitted from the pressure chamber 28 via the transverse pin 34 and the stop washer 40 to the end face of the elastomer part 42 due to the very low compressibility of the thin layer D of elastomer material arranged on the projection 46 acts on the top surfaces of the pin-shaped extensions 48 of the projection 46 formed on the part 44 with almost no delay. The rigid material of the Part 44 does not permit any further axial displacement of the stop ring disk 40 and thus also of the transverse pin 34, so that the central valve 20 opens reliably against a high overpressure and while maintaining a precisely defined opening point with respect to the position of the piston 18.

The sealing element 16 'shown in FIG. 3 differs from the sealing element 16 used in the previously described first embodiment only in that instead of the pin-shaped extensions 48 there is a single, ring-shaped closed extension 54, one opposite the one below arranged part of the projection 46 has a smaller cross-sectional dimension. The dome-shaped elevations 49 are arranged on the end face of the elastomer part 42 above the extension 54 and are evenly spaced apart from one another in the circumferential direction. The function of the sealing element 16 'corresponds to that of the sealing element 16.

Claims

claims

1. An annular sealing element for sealingly closing an annular gap between the inner surface of a cylindrical wall and a cylindrical piston which is axially displaceable relative to the latter and which is arranged concentrically therewith, the annular sealing element comprising two annular and axially adjoining parts (42, 44) , of which the first part (42) consists of an elastomer material and the second part (44) consists of a rigid material, the part (44) made of rigid material having an annular circumferential design which is formed in one piece with it and axially into the second part ( 42) has a protruding projection (46) with a radial extent S, which is designed and arranged in such a way that a section of the second part (42) resting on its radially inner flank has a radial wall thickness Si and one on its radially outer flank adjacent portion of the second part (42) has a radial wall thickness S _a and the radial extent S of Projection (46) is at most 70% of the sum of the wall thicknesses Si + S _a , characterized in that the two parts (42, 44) are detachably connected to one another - the ring-shaped circumferential part (44) made of rigid material Projection (46) axially only almost completely penetrates the part (42) made of elastomer material, the part (42) made of elastomer material completely covers the end face of the projection (46), and - the wall thickness Si is approximately equal to the wall thickness S _a .

2. Annular sealing element according to claim 1, characterized in that the radial extent S of the projection (46) is at most 50% of the sum of the wall thicknesses Si + S _a .

3. Annular sealing element according to claim 1 or 2, characterized in that the part (42) made of elastomeric material on its end face has a plurality of dome-shaped elevations (49) spaced apart in the circumferential direction.

4. Annular sealing element according to one of claims 1 to 3, characterized in that the radial extent S of the projection (46) decreases towards its free end.

5. Annular sealing element according to claim 4, characterized in that the reduction of the radial extension S of the projection (46) follows stepwise or continuously.

6. An annular sealing element according to one of the preceding claims, characterized in that the free end of the projection (46) is formed by a series of pin-shaped projections (48) which are preferably spaced apart from one another in the circumferential direction and extend axially.

7. An annular sealing element according to claim 6, characterized in that the dome-shaped elevations (49) are arranged in the axial continuation of the pin-shaped extensions (48).

8. An annular sealing element according to one of the preceding claims, characterized in that the part (44) made of rigid material has a hollow cylindrical extension (50) on its end face facing away from the part (42) made of elastomer material.

9. Master cylinder (10) for a hydraulic vehicle brake system with a housing (12) which has a bore (14) extending along a longitudinal axis (A), one end of which extends from one to the housing (12) of the master cylinder ( 10) belonging End wall and its other, opposite end is sealed by a closure element (16), wherein in the bore (14) adjacent to the closure element (16) a piston (18) operable therethrough is sealed and axially displaceably received has a central valve (20) which enables a fluid connection between a fluid reservoir and a pressure chamber (28) delimited in the bore (14) by the end wall and the piston (18), and by a non-actuated piston (18) a system component (transverse pin 34) acting on the closure element (16) is held in the open position, characterized in that the closure element (16) is an annular sealing element according to one of the preceding claims.